Richard Simmons‘ longtime housekeeper is petitioning to become co-trustee of his estate … claiming Richard’s brother pressured her to turn down the role while she was still grieving the fitness icon’s death.

Teresa Reveles Muro — who says she worked for Richard for nearly 40 years and was the one who found his body back in July — filed a petition Wednesday … claiming just days after Richard died, she, Richard’s brother Leonard, and Leonard’s wife Cathy went to view his body.

Right after this — when Teresa says she was at her most vulnerable — she says Leonard and Cathy took her to the office of the lawyers handling the trust, where she signed a document turning down the co-trustee role.

After consulting an attorney, she now wants to regain the ability to serve as co-trustee of the estate with Leonard … insisting she’s in the best position to execute Simmons’ last wishes.

Muro’s attorneys say they’ve reached out to the law firm handling the trust numerous times since late July, and they’ve seen no specific explanation for why Leonard won’t agree to revoke Muro’s declination and let her serve as co-trustee per Richard’s wishes.

She’s asking the court to appoint her co-trustee and prevent Leonard from selling off Richard’s assets or exploiting his name, image and likeness until the judge rules on her request.

Simmons passed away in July … with cops saying his death was accidental due to complications from the fall, and listed heart disease as a contributing factor. As we told you, he fell in his bathroom and then refused medical assistance the night before he died.